We have designed and experimentally demonstrated a left-handed metamaterial working at microwave frequencies. An inexpensive mechanical-machining technique was used to fabricate a so-called fishnet metamaterial out of metal-dielectric-metal structure. Our proposed metamaterial exhibits a negative refractive index with the W-band of around 85 GHz in both simulation and experiment. The originality brought by our investigated structure is its simplicity in manufacturing and its functioning with a double polarization (TE and TM modes). These make it suitable in many hopeful millimeter applications such as super-resolution-imaging, magnetic resonance imaging, bio-sensing and so on. Furthermore, the use of a flexible and thin dielectric substrate makes our structure very promising for conformal geometric applications (e.g., radar absorbers aboard military aircrafts).